1. Field of the Invention
The present invention relates in general to a shock absorbing structure to be attached to a component of a motor vehicle, such as a door panel or a quarter panel, and more particularly to such a shock absorbing structure which has excellent formability and is able to effectively absorb impact energy when the vehicle component hits a vehicle passenger or driver upon collision from an accident.
2. Discussion of Related Art
Conventionally, a shock absorbing structure is attached to a component of a motor vehicle or other motor vehicle, such as a bumper or an instrument panel, so as to absorb shocks applied to the vehicle and a vehicle passenger or driver, in particular, his or her head, upon collision from an accident, for example, thereby to assure improved safety of the passenger or driver (hereinafter referred to "vehicle passenger").
In recent years, a door panel, a quarter panel and the like are also required to have a shock absorbing function as described above, for absorbing shocks against the pelvic and breast parts of the vehicle passenger, in particular, so as to assure a higher level of safety of the passenger. In particular, a new side impact standard, FMVSS (Federal Motor Vehicle Safety Standards) 214, took effect in the United States, and strict regulations have been imposed on injury levels with respect to the pelvic and breast parts of a dummy passenger, which are actually measured in the side impact test.
To meet the above requirement and standard, there have been various proposals which include: (1) attaching a urethane pad to the inside of a door panel or the rear side of a quarter panel, (2) attaching to such a component a foamed body which has beads and is formed of polypropylene or polystyrene, instead of the urethane pad, (3) re-modeling or re-designing the structure of the door panel, so that the door panel per se functions as a shock absorbing structure, and (4) attaching a rib structure of a synthetic resin to the inside of the door panel or the rear side of the quarter panel.
In the shock absorbing structure according to the above proposal (1), the urethane pad has a limited freedom of design in its configuration or shape and also suffers from insufficient strength, and the pad must therefore be attached to a door panel or a quarter panel, at its entire surface by means of an adhesive or the like. This results in deteriorated handling ease and increased cost of the panel. Further, the urethane pad usually has maximum deformation percentage of as low as about 70%, and the maximum impact energy that can be absorbed by the urethane pad is accordingly limited. In other words, "impact displacement" of the urethane pad is limited to about 70%. Accordingly, the shock absorbing structure using the urethane pad cannot sufficiently absorb a relatively large impact energy. Namely, the impact resilience of the urethane pad is comparatively large, and the load per unit displacement is inevitably large.
In the shock absorbing structure according to the above proposal (2), the foamed body with beads, which is formed of a thermoplastic resin, can be bonded to a desired component by heat application, and can be easily recycled. However, the foamed body of such a thermoplastic resin has relatively low strength and a relatively small impact displacement, and therefore suffers from the same problems as the urethane pad structure according to the proposal (1). Thus, the proposed structure (2) is not satisfactory or desirable for use as a shock absorbing structure.
In the shock absorbing structure according to the above proposal (3), the re-designing of the door panel structure is limited by the desired appearance requirements of the vehicle. That is, the structure of the door panel must be designed so as to absorb the impact energy as needed, while maintaining the required shapes and positions of an arm rest, a loud speaker, a door pocket and the like which are installed or provided on the door panel. It is thus considerably difficult to achieve the object according to the proposal (3).
On the other hand, the rib structure made of a synthetic resin according to the above proposal (4) has a higher degree of freedom in the choice of the shape and material thereof, and may be therefore formed with various mounting holes or attachment members. Therefore, the rib structure can be easily attached by screws or bolts or by fitting engagement, to the inside of the door panel or the rear side of the quarter panel, for example. Alternatively, the rib structure can be formed integrally with a trim or other part of the door panel. Thus, the attachment of the rib structure to a vehicle component can be accomplished with greater ease and efficiency, as compared with the shock absorbing structure having the urethane pad or the foamed body. In addition, the amount of the impact energy that can be absorbed by the rib structure can be freely controlled to a desired value without changing the shape and structure of the door panel.
Examples of the rib structure made of a synthetic resin, which has been conventionally used as a shock absorbing structure for a motor vehicle, include a rib structure for a bumper as disclosed in JP-B2-4-36894, and a rib structure for an instrument panel as disclosed in JP-B2-4-25177. However, these rib structures have some problems as described later, and cannot be used as a shock absorbing structure for a door panel or quarter panel of the motor vehicle, for example.
FIG. 12 shows a rib structure 20 as disclosed in JP-B2-4-36894, which is a hollow body having an integrally formed rib 22. The rib 22 protrudes inwards and has a concave portion 24 which is open outwards. As shown in FIG. 12, the rib structure 20 is accommodated within a bumper 21. The rib structure 20 is formed by blow molding, this process involves a relatively large number of process steps and a cumbersome molding procedure, and tends to suffer from uneven thickness of the formed walls. It is thus difficult to form such a rib structure having sufficiently high shock absorbing capability. Further, the hollow rib structure 20 undergoes different amounts of deformation or displacement at different portions thereof upon application of impact forces thereto in different directions, resulting in a variation in the amount of the impact energy that can be absorbed by the structure 20, depending upon the direction in which the impact energy acts on the structure. Thus, the rib structure 20 cannot be used as a reliable shock absorbing structure.
To minimize the variation in the amount of the impact energy absorbed by the rib structure 20, it is proposed to increase the number of ribs, and arrange those ribs so as to form a grid or lattice structure. When the rib structure 20 is formed of a conventionally used material, however, the thickness of the ribs must be as small as about 0.4-0.6 mm, so as to ensure a desired shock absorbing function. Such thin-walled rib structure cannot be efficiently manufactured in a large quantity.
FIG. 13 shows a rib structure 26 as disclosed in JP-B2-4-25177, which has a planar base plate 28, and a plurality of ribs 30 formed on one surface of the base plate 28 such that the ribs 30 are spaced apart from each other at a suitable spacing interval. The rib structure 26 is attached via an intermediate plate 36 to a pad 34 which serves as a front covering of an instrument panel 32. When an impact force is applied to this rib structure 26, the ribs 30 are deflected, and the amount of the impact energy absorbed by the structure 26 gradually increases with the amount of deflection of the ribs 30. Therefore, the ribs 30 must have a large maximum amount of deflection, so as to increase the amount of the impact energy that can be absorbed by the rib structure 26. This results in an increased size of the whole structure 26, and makes it difficult to install the structure 26 in a relatively small space within a door panel or on the rear side of a quarter panel.
Thus, the rib structure 26 as described above cannot satisfactorily serve as a shock absorbing structure to be installed on a door panel or a quarter panel, for absorbing the impact energy when the door panel or quarter panel hits the pelvic or breast part of a vehicle passenger. To ensure safety of the vehicle passenger by efficient absorption of the impact energy by the shock absorbing structure installed within a limited space, the shock absorbing structure is required to provide impact displacement of at least 80%, and exhibit a stable shock absorbing characteristic (load-displacement characteristic or relationship) that suits a particular component of the motor vehicle to which the shock absorbing structure is applied.
It is generally desirable that the amount of displacement or deflection S of the rib structure and the resilient force or load F produced upon displacement due to an impact force be linearly proportional with each other, as indicated in the graph of FIG. 22A. It is also desirable that the ratio F/S (corresponding to the F-S relationship line as indicated in FIG. 22A) be not greater than 0.5. On the other hand, the conventional rib structure tends to exhibit a load-displacement relationship (F-S relationship) as indicated by curves "a" and "b" in the graph of FIG. 22B. These curves mean a considerably large initial load value, that is, excessively large load value F when the amount of displacement of the rib structure is relatively small.
A rib structure made of a synthetic resin and installed within a door panel is also disclosed in JP-A-6-72153, which is shown in FIG. 23. This rib structure generally indicated at 94 in FIG. 23 is associated with a door trim 92 for a door panel body 90. The rib structure 94 includes a plurality of relatively thin-walled planar ribs 96 formed on the inner surface of the door trim 92 as integral parts of the door trim 92, so as to extend toward the door panel body 90. The ribs 96 are spaced apart from each other and have different height dimensions so that the ribs 96 have different rigidity values.
When an impact force acts on the rib structure 94 in a direction that causes the door panel body 90 and the door trim 92 to move toward each other, the ribs 96 are forced against the door panel body 90. As a result, the ribs 96 having the relatively large height dimensions and relatively small rigidity values are deflected, deformed or fractured, before the ribs 96 having the relatively small height dimensions and relatively large rigidity values. Thus, the total load F on the rib structure 94 increases as the amount of displacement S of the rib structure 94 as a whole increases. Thus, the rib structure 94 is capable of functioning as a shock absorbing structure which exhibits an almost optimum load-displacement characteristic for protecting the pelvic and breast parts of the vehicle passenger.
When the impact force acts on the rib structure 94 in the direction in which the ribs extend in parallel with each other, that is, in the direction perpendicular to the plane of view of FIG. 23, the impact energy can be more or less effectively absorbed by the ribs 96. However, there is a problem when the impact force acts on the rib structure 94 in the direction (vertical direction as seen in FIG. 23) in which the ribs 96 are spaced apart from each other. In this case, the impact energy cannot be sufficiently absorbed by the ribs 96. Thus, the rib structure 94 suffers from a considerable variation in the shock absorbing capability, depending upon the direction of input of the impact force.
Regarding the rib structure 26 shown in FIG. 13, it is also noted that the ribs 30 formed on the base plate 28 desirably have a comparatively small wall thickness so that the ribs 30 are effectively deformed or fractured to efficiently absorb the impact energy. Generally, the rib structure 26 is formed by injection molding or compression molding, which gives the base plate 28 ribs 30 uniform wall thickness over the entire length or surface area thereof, which in turn assures comparatively high shock absorbing stability of the rib structure 26. However, the rib structure 26 suffers from some problems in the process of manufacture as explained below.
When it is desired to increase the impact displacement of the rib structure 26 to improve the shock absorbing capability, or where the rib structure 26 is installed in a relatively large space within a certain component of a motor vehicle, the thin-walled ribs 30 are required to be formed with a comparatively large height dimension. In this case, the cavities which are formed in a mold to form the respective ribs 30 have a comparatively small width dimension corresponding to the thickness of the ribs 30 and a comparatively small depth dimension corresponding to the height dimension of the ribs 30. In molding the rib structure 26, it is difficult to adequately fill those mold cavities with an appropriate molten resin material, and the ribs 30 formed tend to have flaws such as voids and buckling.
For improved shock absorbing stability of the rib structure 26, each rib 30 should desirably have a constant thickness value over the entire height dimension. This means a reduced draft angle of the rib structure 26, which leads to increased difficulty of removing the formed rib structure 26 from the mold in the molding process.
It is also noted that the optimum load-displacement relationship or characteristic of the rib structure as described above varies depending upon the particular environment in which the rib structure is used.